Representative prior art involving window or door units having nailing fins is illustrated in patent 4,578,905, Apr. 1, 1986 and in FIG. 17 of this application. These fins have a bead received in a groove formed in an extruded extension member of the window frame. The fin when in a closed position lies flat against the outer face of the frame member and is nailed in place to hold it until it is used at window installation time when the fin is then pivoted to an open position perpendicular to the plane of the window unit. This arrangement requires extruding a costly groove in the frame extension member and the fins are exposed during shipment resulting in possible damage to them. At installation time a nail has to be removed to allow them to pivot. If window units are in side by side abutting relationship, the fins have to be removed otherwise the windows are spaced apart by the thickness of the fins.
The nailing fin and corner lock of this invention overcome these problems.